Layered structure and electron device that uses such a layered structure, fabrication process thereof, electron device array and dispaly apparatus

ABSTRACT

A layered structure comprises a variable wettability layer including a material that changes a critical surface tension in response to energy provided thereto, the wettability changing layer including at least a high surface energy part of large critical surface tension and a low surface energy part of low critical surface tension, a conductive layer formed on the variable wettability layer at the high surface energy tension part, and a semiconductor layer formed on the variable wettability layer at the low surface energy part.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present invention is based on Japanese priority applications2003-156314 filed on Jun. 2, 2003, 2004-86388 filed on Mar. 24, 2004,and 2004-124292 filed on Apr. 20, 2004, the entire contents of which areincorporated herein as reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to layered structures suitable forthin-film transistors (TFT), and the like, electron devices such as TFTthat uses such a layered structure, fabrication method thereof, electrondevice arrays and display apparatuses.

[0003] A flat panel display apparatus such as a liquid crystal display(LCD) panel, plasma display panel (PDP), organic electro-luminescence(EL) device, and the like, generally includes a part formed bypatterning a thin film layer, as in the case of active devices such asan MIM (metal-insulator-metal) device or TFT or a light-emitting device.

[0004] Meanwhile, a device that uses an organic material for a partthereof or for the entire part thereof draws attention these daysparticularly in view of its advantageous feature of low cost productionand easiness of producing a large area device and further in view ofpossibility of various functions not achieved by conventional inorganicmaterials. For example, Patent Reference 1 noted below proposes a fieldeffect transistor that changes carrier mobility thereof in response toan external physical stimulus such as light or heat by using an organicsemiconductor material.

[0005] Generally, patterning of a thin film layer has been conducted bya photolithographic process. A typical example thereof may be conductedas follows.

[0006] (1) Apply a photoresist on a substrate carrying a thin film layer(resist application process).

[0007] (2) Remove solvent by applying heat (prebaking process).

[0008] (3) Irradiate the photoresist with ultraviolet light via a hardmask patterned by a laser beam or electron beam according to patterndata (exposure process).

[0009] (4) Remove the resist at the exposed part by using an alkalinesolution (developing process).

[0010] (5) Cure the resist at the unexposed part (pattern part) byapplying heat (post baking process).

[0011] (6) Remove the thin film for the part not covered with the resistfilm by immersing the substrate in an etchant or exposing the same to anetching gas (etching process).

[0012] (7) Remove the resist by an alkaline solution or oxygen radicals(resist removal process).

[0013] An active device is obtained after conducting such processes.(1)-(7) for each of the thin film layers forming the device repeatedly.On the other hand, it will be noted that the complexity of the process,which requires also expensive facilities, has increased the cost of theactive devices thus produced.

[0014] On the other hand, attempts have been made on pattern formationby a printing process in the purpose of reducing the fabrication cost ofactive devices. For example, Patent Reference 2 describes a method ofusing an intaglio offset printing process in place of photolithographyat the time of patterning a thin film layer constituting a TFT.

[0015]FIG. 13 shows this conventional method.

[0016] Referring to FIG. 13, a resist 102 is transferred to a transferroller 103 by rotating the transfer roller 103 over a plate 101 thatcarries a number of depressions holding therein the resist 102, and aresist pattern is formed on a thin film 105 formed on a substrate 104 byprinting the resist 102 by way of the transfer roller 103.

[0017] Further, according to Non-Patent Reference 1, there is discloseda method of forming a metal wiring pattern having a width of about 50 μmwith a pitch of about 400 μm by an ink-jet printing process that uses anano-particle ink.

[0018] Non-Patent Reference 2 discloses a method of forming electrodepatterns 111, 112 and 113 in a TFT by an ink-jet process as shown inFIG. 14, wherein it should be noted that the entire layers of the TFTare formed of organic material layers. In FIG. 14, it should be notedthat the electrode layer 110 forms a gate electrode, the electrode layer111 forms a source electrode and the electrode layer 112 forms a drainelectrode. In the example of FIG. 14, it should be noted that a rib 113of hydrophobic material (polyimide) is provided on a glass substrate 114so that there is secured an electrode gap (channel) of 5-10 μm betweenthe source and drain electrodes 111 and 112. The TFT further includes anorganic semiconductor layer 115 and a polymer insulator layer 116.

[0019] Further, according to Patent Reference 3, there is disclosed amethod of forming a conductive film pattern as shown in FIGS. 15A and15B in which a pattern 121 a showing affinity to a liquid and a pattern121 b showing repellence to the liquid are formed on a substrate 121carrying an organic molecular film by decomposing and removing a part ofthe organic molecular film 122 on the substrate selectively by the stepsof: using an ultraviolet radiation; selectively applying a liquid 123containing conductive fine particles to the pattern 121 a; and furtherconducting a thermal annealing process.

[0020] According to this conventional process, the patterns 121 a and121 b of different nature are formed simply by applying ultravioletradiation to the organic molecular film 122 via a photomask. Thereby,the process of forming the semiconductor device is substantiallysimplified.

[0021] Patent Reference 1

[0022] Japanese Laid-Open Patent Application 7-86600

[0023] Patent Reference 2

[0024] Japanese Laid-Open Patent Application 2002-268585

[0025] Patent Reference 3

[0026] Japanese Laid-Open Patent Application 2002 -268585

[0027] Non-patent Reference 1

[0028] SOCIETY FOR INFORMATION DISPLAY 2002 INTERNATIONAL SYMPOSIUMDIGEST OF TECHNICAL PAPER·VolumeXXXIII, p.753˜755

[0029] Non-patent Reference 2

[0030] SOCIETY FOR INFORMATION DISPLAY 2002 INTERNATIONAL SYMPOSIUMDIGEST OF TECHNICAL PAPER·VolumeXXXIII, p.1017˜1019, Science 290,p.2123˜2126(2000)

SUMMARY OF THE INVENTION

[0031] On the other hand, the offset printing process as disclosed inPatent Reference 1 suffers from the problem of large patterning errorthat can reach as much as ±10 μm when the patterning size error andpositioning error are added. It should be noted that this value is forthe case when high precision printing process is used. When a generalpurpose printing process is used, the error can reach as much as ±50 μm.Thus, offset printing is not deemed suitable for formation of finepatterns.

[0032] In the case of the process that uses ink-jet printing as setforth in Non-patent Reference 1, there arises a problem that the maximumresolution achievable by such a process is only 30 μm when an ordinaryink-jet head designed for common printers is used. In this case, thereappears a positional error of as much as ±15 μm.

[0033] The process of Non-patent Reference 2, on the other hand, isadvantageous in that it is possible to form patterns with the resolutionexceeding the resolution limit of ink-jet process by controlling thewettability to the ink by way of control of the surface energy. On theother hand, this process needs the formation of the rib of polyimide,and associated with this, it is required to conduct a very lengthyprocess including the steps of:

[0034] applying a polyimide precursor and baking (polyimide formation);

[0035] applying a photoresist (resist process);

[0036] removing solvents by heating (prebake);

[0037] irradiate ultraviolet radiation via a mask (exposure);

[0038] removing the resist from the exposed part by an alkaline solution(developing);

[0039] curing the resist for the unexposed part (pattern part) by way ofheating (post baking);

[0040] removing the polyimide film by oxygen plasma from the part wherethere is formed no resist (etching);

[0041] removing the resist by a solvent (resist removal).

[0042] Thereby, the advantage of ink-jet process is cancelled out by theincrease of the number of steps.

[0043] In the process of Patent Reference 3, on the other hand, theorganic film 122 has a very small thickness, and from the fact that thefilm 122 does not exist in the pattern 121 a and the substrate 121 isexposed in such a part, the organic film 122 does not perform anyfunction of bulk material other than the surface energy control, and thefunction achieved according to such a process is limited.

[0044] The object of the present invention is to provide a layeredstructure capable of forming a minute pattern by a simple, low-costprocess characterized by high efficiency of material use such as aprinting process, such that the layered structure can perform variousadded functions in addition to pattern formation, as well as ahigh-performance electron device formed easily by using such a layeredstructure. Further, the present invention provides the method of formingthe same as well as an electron device array and a display device.

[0045] In a first aspect of the present invention, there is provided alayered structure comprising:

[0046] a variable wettability layer including a material that changes acritical surface tension in response to energy provided thereto, saidwettability changing layer comprising at least a high surface energypart of large critical surface tension and a low surface energy part oflow critical surface tension;

[0047] a conductive layer formed on said variable wettability layer atsaid high surface energy tension part; and

[0048] a semiconductor layer formed on said variable wettability layerat said low surface energy part.

[0049] The inventor of the present invention has discovered the factthat it becomes possible to form a conductive layer on a variablewettability layer containing a material that changes the criticalsurface tension thereof in response to energy provided theretoselectively in a part irradiated with ultraviolet energy and that theremaining part (low surface energy part) of such a material not providedwith energy forms an interface excellent for contacting with asemiconductor material, particularly an organic semiconductor material.The inventor of the present invention further confirmed that a highperformance electron device can be provided by a simple fabricationprocess by using such a layered structure.

[0050] Thus, according to the present invention, it becomes possible toprovide the layered structure such that the layered structure carries aminiaturized conductive pattern and a semiconductor layer of largecarrier mobility by a simple and low cost process of high efficiency ofmaterial use, such as a printing process.

[0051] In a second aspect of the present invention, there is provided alayered structure as set forth in the foregoing first aspect in whichthere exists a difference of critical surface tension of 10 mN/m or morein the variable wettability layer between the low surface energy partand the high surface energy part.

[0052] In order to adsorb the liquid containing the conductive materialselectively and positively on the high energy surface part in conformitywith the pattern of the high surface energy part and the low surfaceenergy part, it is necessary that there exists a large surface energydifference or more specifically a large difference of critical surfacetension between these parts. By setting the foregoing different to be 10mN/m or more, it is possible to make sure that the liquid containing theconductive material adheres to the high energy surface part selectively.

[0053] In a third aspect of the present invention, there is provided alayered structure of any of the first or second aspects, wherein the lowsurface energy part of the variable wettability layer has the criticalsurface tension of 40 mN/m or less.

[0054] Because the carrier mobility drops sharply when the criticalsurface tension has exceeded 40 mN/m, it is possible to secure highmobility for the semiconductor layer by setting the critical surfacetension for the low surface energy part to 40 mN/m or less. Further, bysetting the critical surface tension to 40 mN/m or less for the lowsurface energy part, repellence of the liquid at the low energy surfacepart is improved and it becomes possible to provide the layeredstructure without defective conductor patterns.

[0055] In a fourth aspect of the present invention, there is provided alayered structure of any of the first through third aspect, wherein thevariable wettability layer is formed of two or more materials.

[0056] By using materials of different characteristics, it becomespossible to provide a property other than the variable wettability tothe variable wettability layer.

[0057] In a fifth aspect of the present invention, there is provided alayered structure as set forth in any of the first through fourth aspectwherein there is provided a distribution of materials in a thicknessdirection thereof.

[0058] By providing such a distribution, it becomes possible to realizethe desired variable wettability that changes the critical surfacetension in response to energy provided thereto reliably and positively.

[0059] In a sixth aspect of the present invention, there is provided alayered structure of any of the first through fifth aspect, wherein thevariable wettability layer comprises at least a first material havingrelative excellence in electric insulation and a second material havingrelative excellence in the magnitude of change of the critical surfacetension in response to energy provided thereto.

[0060] Thus, it becomes possible to provide a layered structure havingexcellent electric insulation and simultaneously capable of forming fineconductor patterns thereon.

[0061] In a seventh aspect of the present invention, there is provided alayered structure of any of the first through sixth aspect wherein thevariable wettability layer comprises a polymer material having ahydrophobic group on a side chain.

[0062] By forming the variable wettability layer by such a polymermaterial having a hydrophobic group on the side chain, it becomespossible to provide the layered structure to have a semiconductor layerof higher carrier mobility.

[0063] In an eighth aspect of the present invention, there is provided alayered structure of the seventh aspect, wherein the polymer materialhaving the hydrophobic group on the side chain comprises a polymermaterial containing polyimide.

[0064] By using polyimide not only having the characteristic ofexcellent electric insulation but also including a hydrophobic group, itbecomes possible to provide the layered structure of highly insulativenature and capable of being formed with fine conductive patterns.

[0065] In a ninth aspect of the present invention, there is provided alayered structure of any of the first through eighth aspect wherein thesemiconductor layer comprises an organic semiconductor.

[0066] By using an organic semiconductor, it is possible to realizeexcellent interface characteristics for the interface between thevariable wettability layer and the semiconductor layer.

[0067] In a tenth aspect of the present invention, there is providedlayered structure of any of the first through ninth aspect, whereinultraviolet radiation is provided as the energy that causes the changeof the critical surface tension.

[0068] By using ultraviolet irradiation, it becomes possible to formminute conductive layer patterns by a process conducted in theatmospheric ambient without causing damages in the layered structure.

[0069] In an eleventh aspect of the present invention, there is provideda method of forming a layered structure, comprising the steps of:

[0070] forming a variable wettability layer by a material that changes acritical surface tension thereof in response to energy provided thereto;

[0071] forming a pattern by providing energy to a part of said variablewettability layer such that the variable wettability layer includes alow surface energy part having a low critical surface tension and a highsurface energy part having a high critical surface tension;

[0072] forming a conductive layer on said high energy surface part ofsaid variable wettability structure by providing a liquid containing aconductive material to a surface of said variable wettability layerformed with said pattern; and

[0073] forming a semiconductor layer on said low energy surface part ofsaid variable wettability structure.

[0074] Thus, it becomes possible to form the layered structure havingminute conductive layer patterns and a semiconductor layer of highcarrier mobility by a simple and low cost process of high efficiency ofmaterial use such as a printing process.

[0075] In a twelfth aspect of the present invention, there is provided amethod of forming the layered structure of the eleventh aspect whereinthe liquid containing the conductive material is applied to the surfaceof the variable wettability layer by an ink-jet process.

[0076] By using ink-jet process that supplies minute droplets of theliquid, the liquid layer formed on the variable wettability layerexperiences more influence of the surface energy of the variablewettability layer, and the nature of the variable wettability layer inthe layered structure is utilized more effectively.

[0077] In a thirteenth aspect of the present invention, there isprovided a method of forming the layered body of the eleventh or twelfthaspect wherein ultraviolet radiation is used as the energy for causingchange of the critical surface tension.

[0078] By using ultraviolet radiation, it becomes possible to formminute patterns of the conductive layer in the atmospheric ambientwithout causing damages in the interior of the layered structure.

[0079] In an electron device of the fourteenth aspect, there is providedan electron device including a layered structure of any of the firstthrough tenth aspect as a constituent element.

[0080] Thus, it becomes possible to provide a high-performance electrondevice at low cost with reduced use of resources.

[0081] In a fifteenth aspect of the present invention, there is providedan electron device of the fourteenth aspect, wherein the electron devicecomprises a variable wettability layer, a semiconductor layer formed onthe variable wettability layer, a pair of electrode layers formedadjacent to the semiconductor layer as a conductive layer; an insulatorlayer provided at least adjacent to the semiconductor layer; and anelectrode layer provided adjacent to the insulator layer.

[0082] Thereby, it becomes possible to provide a high-performanceelectron device having a transistor structure with low cost, withreduced use of resources.

[0083] In a sixteenth aspect of the present invention, there is providedan electron device of the fourteenth aspect, wherein the electron devicecomprises an electrode layer, a variable wettability layer formed on theelectrode layer, a semiconductor layer formed on the variablewettability layer, and a pair of electrode layers formed adjacent to thesemiconductor layer as the conductive layer.

[0084] Thereby, it becomes possible to provide a high-performanceelectron device having a transistor structure with low cost with reduceduse of resources. Particularly, it should be noted that the variablewettability layer functions as a gate insulation layer, and thus, thecost of the transistor provided by the electron device is reducedfurther.

[0085] In a seventeenth aspect of the present invention, there isprovided a method of fabricating an electron device of the fifteenthaspect or sixteenth aspect, comprising the steps of:

[0086] forming a pattern including a lower surface energy part and ahigh surface energy part by providing energy to a part of the variablewettability layer; forming a pair of electrode layers on the highsurface energy part by providing a liquid containing a conductivematerial to a surface of the variable wettability layer formed with thepattern; and

[0087] forming the semiconductor layer on the variable wettabilitylayer.

[0088] With this, it becomes possible to minimize the gap or channellength between a pair of electrode layers constituting a sourceelectrode and a drain electrode even when a low cost process of highefficiency of material use such as a printing process is used. Further,it becomes possible to increase the carrier mobility, and as a result,the performance of the transistor provided by the electron device isimproved.

[0089] In an eighteenth aspect of the present invention, there isprovided a method of fabricating an electron device of the seventeenthaspect, wherein the liquid containing the conductive material isprovided to the surface of the variable wettability layer is conductedby an ink-jet process.

[0090] By employing an ink-jet process that supplies minute droplets ofthe liquid, the effect of surface energy of the variable wettabilitylayer increases, and thus, the present invention is advantageous for thefabrication of the layered structure that utilizes the feature of thevariable wettability layer.

[0091] In a nineteenth aspect of the present invention, there isprovided a method of fabricating an electron device of the seventeenthor eighteenth aspect wherein the energy for causing change of thecritical surface tension is provided by way of irradiation ofultraviolet radiation.

[0092] Thus, by using ultraviolet radiation, it becomes possible toprovide a fabrication method of an electron device capable of formingthe gap (channel length) between a pair of electrode layers constitutinga source electrode and a drain electrode by a process conducted in anatmospheric ambient without causing damages in the interior of thelayered structure.

[0093] In a twentieth aspect of the present invention, there is providedan array of electron devices in which the electron device of thefourteenth through sixteenth aspect is provided on a substrate withplural numbers.

[0094] Thus, it becomes possible to provide a high-performance electrondevice array with low cost and with reduced use of resources.

[0095] In a twenty-first aspect of the present invention, there isprovided a display device that uses the electron device array of thetwentieth aspect.

[0096] With this, it becomes possible to provide a display device ofhigh image quality at low cost with reduced use of resources.

[0097] According to the first aspect of the present invention made bythe inventor based on the discovery that it becomes possible to form aconductive layer on a variable wettability layer containing a materialthat changes the critical surface tension thereof in response to energyprovided thereto selectively in a part irradiated with ultravioletenergy and that the remaining part (low surface energy part) of such amaterial not provided with energy forms an interface excellent forcontacting with a semiconductor material, particularly an organicsemiconductor material, and that a high performance electron device canbe provided by a simple fabrication process by using such a layeredstructure, the layered structure comprises: a variable wettability layerincluding a material that changes a critical surface tension in responseto energy provided thereto, said wettability changing layer comprisingat least a high surface energy part of large critical surface tensionand a low surface energy part of low critical surface tension; aconductive layer formed on said variable wettability layer at said highsurface energy tension part; and a semiconductor layer formed on saidvariable wettability layer at said low surface energy part, and thus, itbecomes possible to provide the layered structure such that the layeredstructure carries a miniaturized conductive pattern and a semiconductorlayer of large carrier mobility by a simple and low cost process of highefficiency of material use, such as a printing process.

[0098] To ensure the adsorption of the liquid containing the conductivematerial selectively on the high energy surface part in conformity withthe pattern of the high surface energy part and the low surface energypart, it is necessary that there exists a large surface energydifference, or more specifically a large difference of critical surfacetension, between these parts. By setting the foregoing different to be10 mN/m or more as set forth in the second aspect of the presentinvention, it is possible to make sure that the liquid containing theconductive material adheres to the high energy surface part selectively.

[0099] Because the carrier mobility drops sharply when the criticalsurface tension has exceeded 40 mN/m, it is possible to secure highmobility for the semiconductor layer by setting the critical surfacetension for the low surface energy part to 40 mN/m or less as set forthin the third aspect of the present invention. Further, by setting thecritical surface tension to 40 mN/m or less for the low surface energypart, repellence of the liquid at the low energy surface part isimproved and it becomes possible to provide the layered structurewithout defective conductor patterns.

[0100] By using materials of different characteristics in the layeredstructure as set forth in the fourth aspect of the present invention, itbecomes possible to provide a property other than the variablewettability to the variable wettability layer.

[0101] By providing a distribution of materials in the layered structurein the thickness direction thereof as set forth in the fifth aspect ofthe present invention, it becomes possible to realize the desiredvariable wettability that changes the critical surface tension inresponse to energy provided thereto reliably and positively.

[0102] By forming the layered structure of any of the first throughfifth aspect such that the variable wettability layer comprises at leasta first material having relative excellence in electric insulation and asecond material having relative excellence in the magnitude of change ofthe critical surface tension in response to energy provided thereto asset forth in the sixth aspect of the present invention, it becomespossible to provide a layered structure having excellent electricinsulation and simultaneously capable of forming fine conductor patternsthereon.

[0103] By forming the variable wettability layer of the layeredstructure of any of the first through sixth aspect such that thevariable wettability layer comprises a polymer material having ahydrophobic group on a side chain as set forth in the seventh aspect ofthe present invention, it becomes possible to provide the layeredstructure to have a semiconductor layer of higher carrier mobility.

[0104] By using polyimide not only having the characteristic ofexcellent electric insulation but also including a hydrophobic group forthe polymer material in the layered structure of the seventh aspect asset forth in the eighth aspect of the present invention, it becomespossible to provide the layered structure of highly insulative natureand capable of being formed with fine conductive patterns.

[0105] By using an organic semiconductor for the semiconductor layer inthe layered structure of any of the first through eighth aspect as setforth in the ninth aspect of the present invention, it is possible torealize excellent interface characteristics for the interface betweenthe variable wettability layer and the semiconductor layer.

[0106] By using ultraviolet irradiation as the energy that causes thechange of the critical surface tension in the layered structure of anyof the first through ninth aspect as set forth in the tenth aspect ofthe present invention, it becomes possible to form minute conductivelayer patterns by a process conducted in the atmospheric ambient withoutcausing damages in the layered structure.

[0107] According to the method of forming the layered body of theeleventh aspect of the present invention, it becomes possible to formthe layered structure having minute conductive layer patterns and asemiconductor layer of high carrier mobility by a simple and low costprocess of high efficiency of material use such as a printing process.

[0108] By using ink-jet process that supplies minute droplets of theliquid in the method of forming the layered structure of the eleventhaspect as set forth in the twelfth aspect of the present invention, theliquid layer formed on the variable wettability layer experiences moreinfluence of the surface energy of the variable wettability layer, andthe nature of the variable wettability layer in the layered structure isutilized more effectively.

[0109] By using ultraviolet radiation in the method of forming thelayered body of the eleventh or twelfth aspect as set forth in thethirteenth aspect of the present invention, it becomes possible to formminute patterns of the conductive layer in the atmospheric ambientwithout causing damages in the interior of the layered structure.

[0110] According to the electron device of the fourteenth aspect, thereis provided an electron device including a layered structure of any ofthe first through tenth aspect as a constituent element, and thus, itbecomes possible to provide a high-performance electron device at lowcost with reduced use of resources.

[0111] According to the fifteenth aspect of the present invention, itbecomes possible to provide a high-performance electron device having atransistor structure with low cost, with reduced use of resources.

[0112] According to the sixteenth aspect of the present invention, itbecomes possible to provide a high-performance electron device having atransistor structure with low cost with reduced use of resources.Particularly, it should be noted that the variable wettability layerfunctions as a gate insulation layer, and thus, the cost of thetransistor provided by the electron device is reduced further.

[0113] According to the seventeenth aspect of the present invention, itbecomes possible to minimize the gap or channel length between a pair ofelectrode layers constituting a source electrode and a drain electrodeeven when a low cost process of high efficiency of material use such asa printing process is used. Further, it becomes possible to increase thecarrier mobility, and as a result, the performance of the transistorprovided by the electron device is improved.

[0114] By employing an ink-jet process that supplies minute droplets ofthe liquid in the method of fabricating an electron device of theseventeenth aspect as set forth in the eighteenth aspect of the presentinvention, the effect of surface energy of the variable wettabilitylayer increases, and thus, the present invention is advantageous for thefabrication of the layered structure that utilizes the feature of thevariable wettability layer.

[0115] By using ultraviolet radiation in the method of fabricating anelectron device of the seventeenth or eighteenth aspect as set forth inthe nineteenth aspect of the present invention, it becomes possible toprovide a fabrication method of an electron device capable of formingthe gap (channel length) between a pair of electrode layers constitutinga source electrode and a drain electrode by a process conducted in anatmospheric ambient without causing damages in the interior of thelayered structure.

[0116] According to the twentieth aspect of the present invention, thereis provided an array of electron devices in which the electron device ofthe fourteenth through sixteenth aspect is provided on a substrate withplural numbers, and thus, it becomes possible to provide ahigh-performance electron device array with low cost and with reduceduse of resources.

[0117] According to the twenty-first aspect of the present invention,the display device uses the electron device array of the twentiethaspect, and thus, it becomes possible to provide a display device ofhigh image quality at low cost with reduced use of resources.

[0118] Other objects and further features of the present invention willbecome apparent from the following detailed description when read inconjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0119]FIG. 1 is a schematic cross-sectional diagram showing a layeredstructure according to an embodiment of the present invention;

[0120]FIG. 2 is a schematic diagram showing the state in which a liquiddroplet forms an equilibrium state on a solid surface with a contactangle θ;

[0121]FIG. 3 is a diagram showing the relationship between a surfacetension and a contact angle according to a Zisman plotting for the partwhere no ultraviolet radiation is applied and the part where ultravioletradiation is applied for the case a polyimide having a side chain isused for a variable wettability layer;

[0122]FIG. 4 is a diagram showing the relationship between a criticalsurface tension and carrier mobility of an electron device (TFT) for thecase the material of the variable wettability layer is changed;

[0123]FIG. 5 is a schematic diagram showing an example of the polymermaterial having a hydrophobic group in a side chain;

[0124]FIGS. 6A-6D are diagrams showing the fabrication process of alayered structure;

[0125]FIG. 7 is a diagram showing an example of the electron device in across-sectional view;

[0126]FIG. 8 is a diagram showing another example of the electron devicein a cross-sectional view;

[0127]FIG. 9A is a diagram showing an electron device array in across-sectional view while FIG. 9B is a plan view of the electron devicearray showing location of the electrodes;

[0128]FIG. 10 is a diagram showing an example of a display device in across-sectional view;

[0129]FIG. 11 is a diagram showing the relationship between ultravioletirradiation dose and a contact angle against water;

[0130]FIG. 12 is a diagram showing another example of the display devicein a cross-sectional view;

[0131]FIGS. 13A-13C are diagrams showing the process of intaglio offsetprinting disclosed in Patent Reference 2;

[0132]FIG. 14 is a diagram showing an example of a TFT according toPatent Reference 2 in a cross-sectional view;

[0133]FIGS. 15A and 15B are cross-sectional diagrams showing the processof conductive film pattern formation according to Patent Reference 3;

[0134]FIG. 16 is a schematic diagram showing an example of the variablewettability layer in a cross-sectional view;

[0135]FIG. 17 is a schematic diagram showing another example of thevariable wettability layer in a cross-sectional view;

[0136]FIG. 18 is a schematic diagram showing further example of thevariable wettability layer in a cross-sectional view;

[0137]FIG. 19 is a schematic diagram showing the surface of a variablewettability layer in a plan view;

[0138]FIG. 20 is a schematic diagram showing the surface of anothervariable wettability layer in a plan view;

[0139]FIG. 21 is a schematic diagram showing the surface of anothervariable wettability layer in a plan view; and

[0140]FIG. 22 is a cross-sectional diagram showing another example ofthe display device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0141] Hereinafter, an embodiment of the present invention will bedescribed with reference to FIGS. 1 through 12 and FIGS. 16 through 22.

[0142] [Layered Structure]

[0143] First, the layered structure according to an embodiment of thepresent invention will be described.

[0144]FIG. 1 is a schematic cross-sectional diagram showing theprinciple of the present invention for a layered structure 1.

[0145] Referring to FIG. 1, the layered structure 1 of the presentembodiment is constructed on a variable wettability layer 2 formed on asubstrate not illustrated. Here, it should be noted that the variablewettability layer 2 is a layer that changes a critical surface tensionthereof in response to injection of energy thereto. In the illustratedexample, the variable wettability layer 1 includes at least two parts ofdifferent critical surface tension values: a high surface energy part 3having a larger critical surface tension value; and a low surface energypart 4 of lower critical surface tension value.

[0146] It should be noted that there are provided two high surfaceenergy parts 3 in the layered structure 1, wherein a minute gap of 1-5μm is formed between these high surface energy parts 3. Each of the highsurface energy parts 3 of the variable wettability layer 2 is providedwith a conductive layer 5, and a semiconductor layer 6 is provided tothe variable wettability layer 2 such that the semiconductor layer 6adjoins the low surface energy part 4.

[0147] Here, it should be noted that the variable wettability layer 2may be formed of a single material or two or more materials. In the caseof forming the variable wettability layer 2 from two or more materials,in particular, it is possible to provide the variable wettability layer2 in the form of a layer of excellent electrical insulation and havinglarge variation of wettability, by admixing a material of largewettability change to an electrically insulating material.

[0148] By using two or more materials for the variable wettability layer2, it becomes further possible to use a material such as the one havinga large wettability change but poor performance in film formation.Thereby, the possibility of choosing the material is increased. Forexample, it is possible to mix a material having a large change ofwettability but poor performance of film formation due to large cohesivepower with a material having excellent performance for film formation toform the desired variable wettability layer easily.

[0149]FIG. 16 shows the variable wettability layer 2 of the presentembodiment in a cross-sectional view.

[0150] Referring to FIG. 16, it can be seen that there is provided astructure by a first material layer 71 and a second material layer 72,the first material layer having the nature of excellent insulator ascompared with the second material layer 72, the second material layer 72showing superior performance of changing the wettability over the firstmaterial layer, such that the second material layer 72 is provided onthe first material layer 71 in such a manner that there exists a clearboundary between the first material layer 71 and the second materiallayer 72.

[0151] It should be noted that such a structure can be formed by firstforming the first material layer 71, followed by laminating the secondmaterial layer 72 on the first material layer 71. Formation of the firstand second material layers may be conducted by a vacuum process such asvacuum evaporation deposition process, and the like, or alternatively bya coating process that uses a solvent.

[0152] Further, it is possible to form such a structure by the processof applying a solution of the material of the first layer 71 and thematerial of the second layer 72, and applying a drying processthereafter. In the case any of polarity or molecular weight of thematerial forming the second layer 72 is relatively small, the materialof the second layer 72 migrates to the surface of the coated layer andforms the layer 72 therein during the interval in which the film isdried by evaporating the solvent.

[0153] On the other hand, in the case a coating process is used for theformation of the layered structure of FIG. 16, it is often the case thatthere is not formed a clear boundary between the layers 71 and the 72 asrepresented in the schematic cross-sectional diagram of FIG. 17.

[0154] In the present embodiment, it should be noted that the firstmaterial layer 71 having excellent property as an insulator and thesecond material layer 72 providing large change of wettability are usedwith a ratio of 50/50-99/1 (layer 71/layer 72) by weight. Withincreasing weight ratio of the second material layer 72, the property ofthe variable wettability layer 2 as an insulator decreases and the usethereof for an insulator layer of an electron device becomesinappropriate. On the other hand, when the weight ratio of the firstmaterial layer 71 increases, the variation of wettability decreases, andthus the patterning of the conductor layer tend to become poor. Thus, itis preferable to use the first material layer 71 and the second materiallayer 72 with a mixing ratio of 60/40-95/5, more preferably with amixing ratio of 70/30-90/10 by weight.

[0155] As shown in the cross-sectional diagram of FIG. 17, it is notnecessary that the first material layer 71 and the second material layer72 are defined clearly from each other by an interface. Further, asshown in FIG. 17 or 18, it is possible that the first and secondmaterial layers 71 and 72 coexist in the thickness direction with apredetermined concentration distribution.

[0156] In the case the variable wettability layer 2 is formed of two ormore materials, the variable wettability layer 2 may have a layeredstructure of two or more layers. Alternatively, the variable wettabilitylayer 2 may have a single layer structure but with a predeterminedconcentration distribution formed therein in the thickness direction.

[0157] It is preferable that the variable wettability layer 2 has asurface 2 a at the side not contacting with the substrate such that thesecond material layer spreads uniformly over the surface 2 a asrepresented in the plan view of FIG. 19. On the other hand, in the casewhere it is possible to conduct miniaturized patterning, it is possiblethat the first material 71 distributes in the second material layer 72covering the surface 2 a of the variable wettability layer 2 uniformlyas represented in FIG. 20. In this case, the first material 71 may forma domain structure in the second material layer 72 as shown in FIG. 21.

[0158] Here, it should be noted that the conductive layer is preferablya layer obtained by solidifying a liquid containing a conductivematerial by heating or ultraviolet irradiation. Here, the liquidcontaining a conductive material may be any of:

[0159] 1) a solution in which the conductive material is dissolved in asolvent;

[0160] 2) a precursor of the conductive material or a solution in whichthe precursor is dissolved in a solvent;

[0161] 3) conductive particles dispersed in a solvent;

[0162] 4) precursor particles of the conductive material dispersed in asolvent, and the like.

[0163] More specifically, it is possible to use fine particles of ametal such as Ag, Au, Ni, and the like, dispersed in an organic solventor water. Further, it is possible to use an aqueous solution of dopedpolyaniline (PANI) or a conductive polymer in which polystyrenesulfonate (PSS) is doped to polyethylene dioxythiophene (PEDOT).

[0164] It should be noted that the variable wettability layer 2 is alayer that changes the critical surface tension in response to injectionof energy such as heat, ultraviolet radiation, electron beam, plasma,and the like. Thereby, it is preferable to use the one that shows alarge change of critical surface tension before and after the energyinjection.

[0165] In such a material, it should be noted that the liquid containinga conductive material adheres to the high surface energy part 3 havingaffinity to the liquid and is repelled from the low surface energy part4 that shows repellence to the liquid, wherein the high energy surfacepart 3 and the low energy surface part 4 are formed in the form ofpatterns having respective, mutually different critical surface tension,by way of injecting energy to a part of the variable wettability layer.Thus, the conductive layer 5 is formed by causing to adhere the liquidcontaining the conductive material to the high energy surface part 3having affinity to the liquid selectively and further by solidifying theliquid thus adhered.

[0166] Here, wettability (adherence) of the liquid to a solid surface isnoted.

[0167]FIG. 2 shows the state in which a droplet 12 is in equilibrium ona surface of a solid 11 with a contact angle θ. In this state, a Young'sequation holds as follows.

γ_(S)=γ_(SL)+γ_(L) cos θ  (1)

[0168] wherein γ_(S) represents the surface tension of the solid 11,while γ_(SL) represents the surface tension between the solid 11 and theliquid (droplet 12), and γ_(L) represents the surface tension of theliquid (droplet 12).

[0169] It should be noted that surface tension is substantiallyequivalent to surface energy and takes the same value as the surfaceenergy. In the case of cos θ=1, θ becomes 0°, and the liquid or droplet12 wets the solid surface 11 completely. In this case, the value ofγ_(L) becomes γ_(S)-γ_(SL), and this is called the critical surfacetension γ_(c) of the solid 11. The value of γ_(c) can be determinedeasily by using several kinds of liquids of known surface tension valuesto form a Zisman plot in which the relationship between the surfacetension of the droplet 12 and the contact angle is plotted and obtainingthe surface tension value for θ=0°(cos θ=1). It should be noted that thesurface of the solid 11 having a large value for γ_(c) and hence showingaffinity to the liquid is easily wetted by the liquid droplet 12, whilethe surface of the solid 11 having a small value for γ_(c) is wettedlittle by the liquid droplet 12 (repellent).

[0170] The measurement of the contact angle θ is conveniently achievedby using a droplet method. In the droplet method, there are variousmethods such as:

[0171] (a) a tangential method that reads the contact angle of thedroplet 12 by a microscope by focusing the cursor of the microscope tothe contact point of the liquid 12;

[0172] (b) a θ/2 method in which an angle θ/2 formed by the lineconnecting the apex of the droplet 12 and the contact edge of thedroplet 12 and the surface line of the solid 11 is obtained by focusingthe cross point of the microscope cursor to the apex and aligning one ofthe cursor lines to the edge of the droplet. The angle θ is thenobtained by doubling the value θ/2 thus obtained; and

[0173] (c) a three-point click method in which the droplet 12 isdisplayed on a monitor screen and a point on the circumference,preferably the apex, and two contact points of the droplet and the solid11 are clicked. Thereafter, the angle θ is obtained by image processing.

[0174] The reliability of the contact angle θ increases in the order of(a)→(b)→(c).

[0175]FIG. 3 shows an example of the Zisman plot for the case of using apolyimide having a side chain to be described later with reference toExample 1 for the variable wettability layer 2, wherein FIG. 3 shows theZisman plot for both the part not exposed to the ultraviolet radiationand the part exposed to the ultraviolet radiation.

[0176] Referring to FIG. 3, it will be noted that the critical surfacetension γ_(c) of the part not exposed to the ultraviolet radiation hasthe value of about 24 mN/m, while the critical surface tension γ_(c) ofthe part exposed to the ultraviolet radiation has the value of about 45mN/m. Thereby, there is a difference of Δγc of about 21 mN/m betweenthese two parts.

[0177] In order to make sure that the liquid containing the conductivematerial adheres selectively and reliably only to the high energysurface part 3 in the pattern formed of the high energy surface part 3and the low energy surface part 4, it is necessary to secure a largesurface energy difference, and hence a large difference Δγc of criticalsurface tension between the parts 3 and 4.

[0178] Table 1 shows the result of evaluation for the relationshipbetween Δγc between the energized part and non-energized part and theselective adherence of polyaniline (water-soluble conductive polymer)for the case the variable wettability layer 2 is formed on a glasssubstrate by using various materials.

[0179] In Table 1, it should be noted that the selectivity of adhesionis evaluated by dropping an aqueous solution of polyaniline on an areaincluding a pattern boundary of an energized part and a non-energizedpart and observing the existence (defective pattern) or non-existence ofpolyaniline on the non-energized part after removal of excess solution.In Table 1, it should be noted that A represents polyvinylphenolsupplied from Maruzen Petrochemical Co. Ltd. as trade name MARUKALYNCUR; B represents a polyimide marketed from Nissan ChemicalIndustries Limited under the trade name RN-1024; C representsfluorine-containing acrylate polymer marketed from Asahi Glass Co. Ltdunder the trade name AG-7000; and D represents a polyimide having a sidechain marketed from Chisso Corporation under the trade namePIA-X491-E01. TABLE 1 Material Energy Δ γ c Pattern evaluation A: UV  6mN/m x extensive depo in polyvinylphenol non-energized part B: polyimideUV 10 mN/m - slight depo in non-energized part C: F-acrylate Heat 15mN/m - no depo in non- polymer energized part D: polyimide UV 21 mN/m -no depo in non- with side chain energized part

[0180] Table 1 indicates that it is preferable to set the difference Δγcof the variable wettability layer 2 between low surface energy part 4and to be equal to or lager than 10 mN/m, more preferably to be equal toor larger than 15 mN/m.

[0181] Meanwhile, in the layered structure of the present embodiment, itshould be noted that the semiconductor layer 6 adjoins the low surfaceenergy part 4 of the variable wettability layer 2, and thus, there is apossibility that the property of the low energy surface part 4 providesinfluence on the property of the semiconductor layer 6.

[0182]FIG. 4 shows the relationship between the mobility of thesemiconductor layer 6 and the critical surface tension γ_(c) for thenon-energized part of the variable wettability layer 2 for various TFTsthat are fabricated while changing the material of the variablewettability layer 2 used for the gate insulation film.

[0183] Referring to FIG. 4, A represents the case in which a polyimidehaving a side chain is used, B represents the case in which apolyvinylphenol is used, C represents the case in which an organicsilica is used, D represents the case in which a thermal oxide film isused, E represents the case a polyimide is used and F represents thecase a sputtered SiO₂ film is used. In the investigation, it should benoted that the source electrode 5 a and the drain electrode 5 b of theTFT were formed by liftoff of an Au film formed by an evaporationdeposition process.

[0184] From FIG. 4, it can be seen that the carrier mobility dropssharply when the critical surface tension γ_(c) has exceeded 40 mN/m.Thus, it is preferable to set the critical surface tension γ_(c) to be40 mN/m or less for the low surface energy part of the variablewettability layer 2.

[0185] On the other hand, when the critical surface tension γ_(c) issmaller than 20 mN/m, most of the solvents are repelled, and thus, it ispreferable to control the critical surface tension γ_(c) to be 20 mN/mor more when forming the semiconductor layer 6 by a coating process.

[0186] For the variable wettability layer 2, it is preferable to use apolymer material having a hydrophobic group on the side chain thereof.More specifically, it is preferable to use a polymer material in which aside chain R having a hydrophobic group is bonded to a main chain L ofpolyimide or (meta) acrylate directly or via a coupling group (notshown), as represented in the schematic diagram of FIG. 5.

[0187] For the hydrophobic group, it is possible to use the one having aterminating structure of —CF₂CH₃, —CF₂CF₃, —CF(CF₃)₂, —CF(CF₃)₃, —CF₂H,—CFH₂, and the like. In order to facilitate alignment of the molecularchains with each other, it is preferable to use a group having a longcarbon chain, preferably having the number of carbon atoms of four ormore. Particularly, it is preferable to use a polyfluoroalkyl groupdesignated hereinafter as Rf group in which two or more hydrogen atomsin the alkyl group are substituted with a fluorine atom. Particularly,the use of Rf group having 4-20 carbon atoms is preferable. Amongothers, it is preferable to use an Rf group having 6-12 carbon atoms.

[0188] While the Rf group may have any of a straight chain structure ora branched structure, it is preferable to use the straight chainstructure for the Rf group in the present embodiment.

[0189] Further, it is preferable to use a perfluoro alkyl group in whichsubstantially all the hydrogen atoms of the alkyl group are substitutedwith a fluorine atom for the hydrophobic group. Particularly, it ispreferable that the perfluoro alkyl group is the one represented asC_(n)F_(2n+1)— where n is an integer of 4-16, and it is more preferableto use the group in which n is 6-12. While the perfluoro alkyl group maybe any of the one having a straight chain structure or a branchedstructure, the group having a straight chain is deemed more preferable.

[0190] With regard to the foregoing materials, reference should be madeto Japanese Laid-Open Patent Application 3-178478. It is known that theforegoing materials have the feature of showing affinity when contactedwith the liquid or solid under an elevated temperature condition andbecoming repellent to the liquid when heated in the atmospheric ambient.Thus, with the use of the foregoing material, it becomes possible tochange the critical surface tension in response to injection of energyupon appropriate selection of the medium to be contacted.

[0191] For the hydrophobic group, it is further possible to use a grouphaving a terminating structure free from fluorine atom such as —CH₂CH₃,—CH(CH₃)₂, —C(CH₃)₂, and the like. In this case, too, it is preferableto use a group having a long carbon chain for facilitating mutualalignment of the molecular chains and it is preferable to use the onehaving four or more carbon atoms. While any of the straight chainstructure and a branched structure can be used for the hydrophobicgroup, it is preferable to use the one having the straight chainstructure. Here, the foregoing alkyl group may contain any of a halogenatom, a cyano group, a phenyl group, a hydroxyl group, carboxyl group,or a phenyl group substituted with an alkyl group or an alkoxy grouphaving a straight chain containing 1-12 carbon atoms, a branched chainor a cyclic structure. The larger the number of the bonding sites of R,the lower the surface energy (smaller critical surface tension), and itis believed that the material becomes more repellent to the liquid. Whenultraviolet irradiation is applied, a part of the bond is disconnectedor the state of alignment changes. Thereby, there is caused increase ofthe critical surface tension, and it is believed that this is the reasonwhey the material changes the affinity to the liquid.

[0192] In view of the fact that a semiconductor layer is to be formed onthe variable wettability layer 2, it is preferable that the polymermaterial having a hydrophobic group on the side chain includespolyimide. Because polyimide has superior resistance against solvent andtemperature, it is possible to avoid the problems such as swellingcaused by solvent or cracking caused by the temperature change at thetime of baking when a semiconductor layer is formed on the variablewettability layer 2.

[0193] Further, in the case of forming the variable wettability layer 2from the materials of two or more kinds, it is also preferable to usepolyimide for the material other than the one having the hydrophobicgroup on the side chain, in view of the resistance to temperature,resistance to solvent, and affinity to the liquid.

[0194] For example, the hydrophobic group used for the polyimide of thepresent embodiment can have any of the structures represented by thechemical formulae 1-5 below.

[0195] wherein X represents —CH₂— or CH₂CH₂— group, A¹ represents any of1,4 cyclohexylene, 1,4 phenylene or 1,4 phenylene substituted with 1-4fluorine atoms, each of A², A³ and A⁴ is individually any of a singlebond, 1,4 cyclohexylene, 1,4 phenylene or 1,4 phenylene substituted with1-4 fluorine atoms, each of B¹, B² and B³ is individually any of asingle bond or a CH₂CH₂— group, B⁴ is an alkylene group containing 1-10carbon atoms, each of R³, R⁴, R⁵, R⁶ and R⁷ is an alkyl group containing1-10 carbon atoms, and p is an integer of 1 or larger.

[0196] wherein each of T and U represents individually any of a benzenering or a cyclohexane ring, and wherein arbitrary number of the hydrogenatoms on these rings may be substituted with an alkyl group having 1-3carbon atoms or a fluorinated alkyl group having 1-3 carbon atoms or anyof F, Cl or CN, each of m and n is an integer of 0-2 individually, h isan integer of 0-5, R is any of H, F, Cl, CN or a monovalent organicgroup, wherein two Us may be the same or different when m is 2 and twoVs may be the same or different when n is 2.

[0197] wherein the linking group Z is any of CH₂, CFH, CF₂, CH₂CH₂ orCF₂O group, while the ring Y is 1,4 cyclohexylene or 1,4 phenylene inwhich 1-4 hydrogen atoms may be substituted with F or CH₃, each of A¹-A³is individually a single bond, 1,4-cyclohexylene or 1,4 phenylene inwhich 1-4 hydrogen atoms may be substituted with F or CH₃, each of B1-B3is individually a single bond, an alkylene group having 1-4 carbonatoms, an oxygen atom, an oxyalkylene group having 1-3 carbon atoms oran alkyleneoxy group having 1-3 carbon atoms, R is any of a hydrogenatom, an alkyl group having 1-10 carbon atoms in which an arbitrary CH₂may be substituted with CF₂, or an alkoxy or alkoxyalkyl group having1-9 carbon atoms in which one CH₂ may be substituted with CF₂, andwherein the bonding position of the amino group to the benzene ring isarbitrary. In the case Z is CH₂, not all of B₁-B₃ can be simultaneouslyan alkylene group having 1-4 carbon atoms. In the case Z is CH₂CH₂ andthe ring Y is 1,4-phenylene, A¹ and A² cannot be a single bond at thesame time. Further, in the case Z is CF₂O, the ring Y cannot be1,4-cyclohexylene.

[0198] wherein R₂ is a hydrogen atom or an alkyl group having 1-12carbon atoms, Z₁ is a CH₂ group, m is 0-2, the ring A is any of abenzene ring or a cyclohexane ring, 1 is 0 or 1, and each Y1 isindividually an oxygen atom or a CH₂ group, and each n₁ is independently0 or 1.

[0199] wherein each Y₂ is individually an oxygen atom or a CH₂ group,and each of R3 and R4 is individually a hydrogen atom or an alkyl groupor a perfluoro alkyl group having 1-12 carbon atoms, at least one beingan alkyl group having three or more carbon atoms or a perfluoro alkylgroup and each n₂ is independently 0 or 1.

[0200] Details of these materials is described in Japanese Laid-OpenPatent Application 2002-162630, 2003-96034 and 2003-267982. With regardto the tetracarbonic acid di-hydrate constituting the principal chainskeleton of these hydrophobic groups, it is possible to use variousmaterials of aliphatic series, alicyclic series, aromatic series, andthe like. More specifically, it is possible to use any of pyromelliticacid di-hydrate, cyclobutanetetracarbonic acid di-hydrate, butanetetracarbonic acid di-hydrate, and the like. In addition, it is possibleto use the materials described in detail in the Japanese Laid-OpenPatent Applications 11-193345, 11-193346, 11-193347, and the like.

[0201] As noted above, the polyimide containing the hydrophobic grouphaving the chemical formulae 1-5 noted above may be used alone or in theform of mixture with other material. In the case of mixing the foregoingmaterial with other material, it is preferable to use also a polyimidefor the other material to be mixed in view of resistance to temperature,resistance to solvent and affinity.

[0202] In addition, it is also possible to use a polyimide containing ahydrophobic group not represented by foregoing chemical formulae 1-5.

[0203] As a result of alignment of the side chains R having thehydrophobic group at the surface, there is obtained an additional effectin the present invention that the interface characteristics of thesemiconductor layer 6 adjoining thereto is improved. This effect isparticularly remarkable when the semiconductor layer is formed of anorganic insulator. Such improvement of the interface characteristicsmeans the effect of: (a) increase of crystal grains in the semiconductorformed of a crystalline body, leading to increase of carrier mobility;(b) decrease of interface states in the semiconductor formed of anamorphous (polymer) material, leading to increase of carrier mobility,too; (c) alignment of the molecular axes of n-conjugate principal chainsin the case the semiconductor is a polymer having a long alkyl sidechain caused by constraint imposed on the alignment, leading to increaseof the carrier mobility, and the like.

[0204] In the present embodiment, it is preferable to set the thicknessof the variable wettability layer 2 to the range of 30 nm-3 μm,particularly to the range of 50-1 μm. When the thickness is smaller thanthe foregoing range, the property of the layer 2 as a bulk material,such as electric insulation, performance as a barrier for gaspenetration, resistance against moisture, and the like, is tend to belost. When the thickness exceeds the foregoing range, on the other hand,the surface morphology of the variable wettability layer 2 isdeteriorated.

[0205] The application of the liquid containing the conductive materialto the surface of the variable wettability layer 2 may be conducted byvarious coating processes such as spin coating process, dip coatingprocess, screen printing process, offset printing process, ink-jetprocess, and the like, wherein the use of ink jet process is deemedparticularly advantageous for increasing the sensitivity to the surfaceenergy of the variable wettability layer 2 in view of the capability ofthe ink-jet process of injecting very small droplets.

[0206] As noted previously, the resolution of ink-jet process is about30 μm and the positional alignment error achievable by this process isabout ±15 μm when a commonly used ink-jet head designed for an ordinaryprinter is used, while in the present invention, it can become possibleto form more fine patterns by utilizing the difference of surface energyin the variable wettability layer 2.

[0207] For the semiconductor layer 6, it is possible to use variousmaterials including an inorganic semiconductor such as CdSe, CdTe, Si,and the like, or an organic semiconductor such as organic low molecularmaterial including pentacene, anthracene, tetracene, phthalocyanine, andthe like, a polyacethylene series conductive polymer, polyparaphenyleneand its derivatives, a polyphenylene series conductive polymer such aspolyphenylene pyrene and its derivatives, polypyrrole and itsderivatives, polythiophene and its derivatives, a heterocyclicconductive polymer such as polyfuran and its derivatives, an ionicconductive polymer such as polyaniline and its derivatives, and thelike, wherein the improvement of performance caused by the variablewettability layer 2 appears most significantly when an organicsemiconductor is used as noted before.

[0208] Further, it is preferable to conduct the injection of energy to apart of the variable wettability layer 2 by ultraviolet irradiation inview of its features of: (a) allowing operation in the atmosphericambient; (b) providing high resolution; and (c) reduced damages to theinterior of the layer.

[0209] [Method of Making Layered Structure]

[0210]FIGS. 6A-6D show an example of the process of making the layeredstructure 1 according to the present embodiment.

[0211] First, as shown in FIG. 6A, the variable wettability layer 2 isformed on a substrate 7 of a glass, a plastic such as polycarbonate,polyarylate, polyether sulfonate, a silicon wafer, a metal, and thelike.

[0212] The variable wettability layer 2 is formed of a material thatchanges the state thereof in response to ultraviolet irradiation fromthe low surface energy state (repellent to the liquid) to the highsurface energy state (showing affinity to the liquid). While thestructure of such a material has already been described, the experimentsmade by the inventor indicate that the material having a polyimideskeleton for the principal chain and a long alkyl side chain shows aparticularly large change of wettability upon ultraviolet irradiation.

[0213] The variable wettability layer 2 can be formed by dissolving ordispersing a polymer or precursor thereof having such a structure intoan organic solvent to prepare a solution and by applying such a solutionto the substrate 7 by a spin coating process, dip coating process,wire-bar coating process, casting process, and the like, followed by abaking process. For example it is possible to use a vertical alignmentmaterial of a liquid display device such as PIA-X491-E01 of ChissoCorporation, SE-1211 of Nissan Chemical Industries Limited, JALS-2021 ofJSR, and the like for this purpose.

[0214] Next, in the step of FIG. 6B, an ultraviolet radiation is appliedto the surface of the variable wettability layer 2 via a mask 8. Withthis, the pattern including the low energy surface part 4 and the highsurface energy part 5 is formed. For the ultraviolet radiation, it ispossible to use a radiation of relatively short wavelength of 100-300nm.

[0215] Next, in the step of FIG. 6C, a liquid containing the conductivematerial is supplied to the variable wettability layer 2 formed with theforegoing pattern by an ink-jet process, and the like. With this, theconductive layer 5 is formed selectively on the high surface energy part3.

[0216] Finally, as shown in FIG. 6D, the semiconductor layer 6 is formedby depositing a low molecular semiconductor on the structure of FIG. 6Cby an evaporation deposition process or by applying a solutiondissolving therein a polymer semiconductor or a precursor thereof by anyof spin coating process, dip coating process, wire-bar coating process,casting process, and the like.

[0217] [Electron Device]

[0218] By using the layered structure 1 thus formed, it becomes possibleto manufacture an electron device such as a diode, transistor,photoelectric conversion device, thermoelectric conversion device, andthe like.

[0219]FIG. 7 shows an electron device 31 according to an embodiment ofthe present invention, wherein the electron device 31 is a field effecttransistor implemented in the form of a TFT.

[0220] Referring to FIG. 7, the substrate 7 and the variable wettabilitylayer 2 are identical to those described previously.

[0221] Thus, the patterns of the low surface energy part 4 and the highsurface energy part 3 are formed in the variable wettability layer 2,and electrode layers 5 a and 5 b are formed on the high surface energypart 3 as a conductive layer, by applying thereto a liquid that containstherein the conductive material. For the liquid containing theconductive material, it is possible to use the one in which metal fineparticles of Ag, Au, Ni, and the like are dispersed in an organicsolvent or water can be used. Alternatively, it is possible to use anaqueous solution of conductive polymer such as doped polyaniline (PANI)or polyethylene dioxythiophene (PEDOT) doped with polystyrene sulfonate(PSS).

[0222] It should be noted that the precision of the gap between theelectrode layers 5 a and 5 b becomes the key for the performance of thedevice of the present embodiment. Because it is possible to form thepattern formed of the low surface energy part 4 and high surface energypart 3 with high precision in the present embodiment, it is possible tosecure high precision for the electrode layers 5 a and 5 b, irrespectiveof the means of providing the liquid.

[0223] Further, the semiconductor layer 6 is formed thereon by any ofspin coating process, dip coating process, casting process, and thelike. For the semiconductor layer 6, it is particularly preferable touse an organic semiconductor material.

[0224] It should be noted that the foregoing constitute the part of theelectron device 31 that includes the layered structure 1 as theconstituent element.

[0225] Further, an insulation layer 32 is formed thereon by any ofevaporation deposition process, CVD process, spin coating process, dipcoating process, casting process, and the like, wherein an inorganicinsulator or an organic insulator can be used for the insulation layer32.

[0226] In the case the semiconductor layer 6 is an organic semiconductormaterial, it is necessary to choose the method of forming the insulationlayer 32 such that damaging to the semiconductor layer 6 is avoided. Forexample, it is preferable to avoid the use of high temperature or highenergy ions, active radicals, or solvents capable of dissolving theorganic semiconductor material when forming the insulation layer 32.From this view point, it is preferable to use SiO₂ formed by anevaporation deposition process, water-soluble PVA (polyvinyl alcohol),alcohol-soluble PVP (polyvinyl phenol), perfluoro polymer soluble to afluorine solvent, and the like.

[0227] Finally, an electrode layer 33 is formed on the insulation layer32 by an evaporation deposition process, CVD process, spin-coatingprocess, dip-coating process, casting process, and the like. Further, itis possible to use various conductive films for the electrode layer 33.In this case, the conductive film is formed uniformly, followed by apatterning process conducted by ordinary photolithographic process.Alternatively, the conductive material may be patterned by a microcontact printing process. Further, it is possible to form the pattern ofthe conductive material by injecting the liquid containing theconductive material bay an ink-jet process.

[0228] As shown from FIG. 7, the electron device 31 functions as a TFT(thin film transistor). Thus, the electrode layers 5 a and 5 b functionas source electrode and drain electrode, the insulation film 32functions as a gate insulation film and the electrode layer 33 functionsas a gate electrode. Thereby, the gap between the electrode layers 5 aand 5 b defines the channel in the semiconductor layer 6.

[0229] Because the present embodiment forms the conductor patterns 5 aand 5 b by surface energy control of the variable wettability layer 2,and thus, it is possible to provide additional functions to the variablewettability layer 2 itself, contrary to the technology that forms therepellant part and affinity part separately as in the case of theconventional art.

[0230] In the example of FIG. 7 in which the variable wettability layer2 covers the surface of the substrate 7, for example, the variablewettability layer 2 functions as a barrier layer against gas or water inthe case the substrate 7 is formed of a material such as a plasticpermeable with gas or water. Thereby, adversary effect of such gas orwater on the electron device 31 can be reduced effectively.

[0231] While the semiconductor layer 6 is formed on the entire surfaceof the substrate in the example of FIG. 7, it is also possible that thesemiconductor layer 6 is patterned to form an island region covering thechannel region. For such patterning of the semiconductor layer 6, it ispossible to use evaporation deposition process that uses a mask, screenprinting process, ink-jet process, micro contact printing process, andthe like.

[0232]FIG. 8 shows an electron device 41 according to another embodimentof the present invention.

[0233] Referring to FIG. 8, the electron device 41 of the presentembodiment is formed by a process including the step of forming anelectrode layer 42 on a substrate of a glass, a plastic such aspolycarbonate, polyacrylate, polyether sulfonate, and the like, asilicon wafer or a metal, by any of evaporation deposition process, CVDprocess, spin coating process, dip coating process, casting process, andthe like, wherein various conductive films can be used for the electrodelayer 42. The electrode layer 42 may be patterned by an ordinaryphotolithography or micro contact printing process after forming tocover the entire surface of the substrate, or alternatively directly inthe form of a conductive layer pattern by supplying a liquid containinga conductive material by an ink jet process, and the like.

[0234] After forming the electrode layer pattern 42, the variablewettability layer 2 is formed on the electrode layer pattern 42similarly. Because this variable wettability layer 2 is used also as agate insulation film, it is preferable that the variable wettabilitylayer 2 has highly insulating nature. Further, it should be noted thatthe variable wettability layer 2 has a two-layered structure includingan upper layer having a large variable wettability and a lower layer ofsmall or no wettability but has excellent nature of insulator. In thevariable wettability layer 2, there is formed a pattern of the lowsurface energy part 4 an the high surface energy part 3 similarly asbefore, and the electrode layers 5 a and 5 b are formed on the highsurface energy part 3 in the form of a conductive layer by applying aliquid containing the conductive material.

[0235] Finally, the semiconductor layer 6 is formed to cover the entiresurface of the structure thus formed or in an island form covering atleast the channel region.

[0236] As is apparent from FIG. 8, the electron device 41 functions as aTFT (thin film transistor). Thereby, the electrode layer 42 forms a gateelectrode, the variable wettability layer 2 forms a gate insulationfilm, the electrode layers 5 a and 5 b form source and drain electrodes,wherein the gap between the electrode layers 5 a and 5 b defines thechannel region of the TFT. Because the variable wettability layer 2functions also as a gate insulation film, the device of FIG. 8 can bemanufactured with a simplified process.

[0237] In the embodiment of FIG. 8, it is also possible to provideanother variable wettability layer (not shown) separately to thevariable wettability layer 2 and use the same for the patterning of theelectrode layer 42.

[0238] [Electron Device Array]

[0239]FIGS. 9A and 9B show an electron device array 51 that uses theelectron device 41 of FIG. 8 wherein FIG. 9A shows the electron devicearray 51 in a cross-sectional view while FIG. 9B shows the electrodesformed on the array 51.

[0240] Referring to the drawings, there are formed a number ofstructures of FIG. 8 in the form of a two-dimensional array, whereineach of the structures or element of the array includes the electrodelayer 42 functioning as the gate electrode, the variable wettabilitylayer 2 functioning also as the gate insulation film and the electrodelayers 5 a and 5 b functioning as the source and drain electrodes.

[0241] Here, it should be noted that each gate electrode 42 of each TFT(electron device 41) is connected to a bus line so as to be driven by adriver integrated circuit supplying a scanning signal. Further, eachsource electrode 5 a of each TFT (electron device 41) is connected to abus line so as to be driven by a driver integrated circuit supplying adata signal.

[0242] Next, the semiconductor layer 6 is formed in the form of islandcovering the channel region by a micro contact printing process, forexample, and with this, the array 51 of the electron device (TFT) iscompleted. It should be noted that a micro contact printing process isthe process that forms a stamp of PDMS (polydimethylsiloxane) by using amaster patterned by a photolithographic process, attach a liquidcontaining a semiconductor material at the projecting part of themaster, and transferring the liquid to the substrate.

[0243] Because the semiconductor layer 7 is formed in the form of anisland covering the channel region, there occurs no leakage of currentto the adjacent devices or elements.

[0244] While not illustrated in FIG. 9, it is preferable to cover theelectron device (TFT) 41 with a passivation film so as to avoiddeterioration of characteristics of the electron device 41 (FT) causedby oxygen, water or radiation.

[0245] For such a passivation film, it is possible to use an aluminumnitride, silicon nitride, silicon oxynitride, and the like, whereinthese materials cam be formed either by a CVD process, an ion platingprocess, and the like.

[0246] [Display Device]

[0247]FIG. 10 shows an example of a display device 61 that uses theelectron device array 51 in a cross-sectional view.

[0248] Referring to FIG. 10, there is provided a display element 64between a substrate 7 carrying thereon the electron device (TFT) array51 and a second substrate 63 carrying a transparent conductive film 62,wherein the display element 4 on the drain electrode 5 b, which actsalso a pixel electrode, is switched by the TFT (electron device 41). Thedisplay element 64 may be any of a liquid crystal device, anelectrophoresis device, an organic EL device, and the like.

[0249] When a liquid crystal display device is used for the displayelement 64, the feature of low power consumption is achieved because ofthe nature of liquid crystal cell of voltage driving. Further, becauseof low drive voltage, it becomes possible to increase the drivefrequency of the TFT, and the display device 61 is suitable for a largecapacity display device. It should be noted that use of any of TN-modedriving, STN-mode driving, guest-host-mode driving, polymer dispersedliquid crystal (PDLC) cell structure, and the like, is possible, whereinit is preferable to use the PDLC cell structure fore the display element64 in view of its bright and white representation when used in areflection mode.

[0250] In a reflection-mode liquid crystal device that carries thedisplay element 64 on the electron device (TFT) array 51, it should benoted that an interlayer insulation film 81 is provided on the electrondevice (TFT) array, and a pixel electrode 83 provided on the interlayerinsulation film 81 makes a connection with the drain electrode 5 b ofthe electron device (TFT) 41 via a contact hole 82.

[0251] An electrophoresic device is a device using a dispersion liquid,wherein the dispersion liquid is a liquid in which particles showing afirst color (such as white color) are dispersed in a colored mediumshowing a second color. With electric charging of the particles of thefirst color in the colored dispersion medium, the particles change thelocation in the dispersion medium upon application of an electric field,and with this, the color represented by the color display element 64changes. According to this display method, a bright representation ofimages with wide viewing angle is realized. Further, because of thememory effect of the representation, the display device that uses theelectrophoresis effect for the display element 64 has the advantageousfeature of low electric power consumption.

[0252] Further, by surrounding the foregoing dispersion liquid by apolymer film to form micro capsules, the operation of representation isstabilized and manufacturing of the display device is facilitated. Themicrocapsules can be formed by various known processes such ascoacervation method, in-situ polymerization method, interfacepolymerization method, and the like.

[0253] For the while color particle, the use of titanium oxide particlesis particularly preferable. According to the needs, surface processingor conjugation with other materials may be made. For the dispersionmedium, it is preferable to use an organic medium of high specificresistance such as aromatic hydrocarbons including benzene, toluene,xylene, naphthene, and the like, or aliphatic hydrocarbons includinghexane, cyclohexane, kerosene, paraffin, and the like, or halogenated(hydro) carbons including trichloroethylene, tetrachloroethylene,trichlorofluoroethylene, ethyl bromide, and the like, or fluorinatedether compound, or fluorinated ester compounds, a silicone oil, or thelike.

[0254] In order to color the dispersion medium, an oil-soluble dyehaving desired absorption characteristics such as anthraquinones or azocompounds. Further, it is possible to add a surfactant to the dispersionliquid for stabilizing the dispersion.

[0255] An organic EL device is a light-emitting type device and canachieve brilliant full color representation. Because the EL layer usedin such an organic EL device is a very thin organic film, an organic ELdevice has the feature of flexibility and is suited for forming on aflexible substrate.

EXAMPLES

[0256] Hereinafter, some examples of the foregoing embodiments aredescribed together with comparative examples.

Example 1

[0257] Example 1 relates to fabrication of an electron device having astructure similar to that of the electron device (TFT) 31 shown in FIG.7.

[0258] First, a mixed solution dissolving therein the precursor of thematerials having the structure shown in chemical formula 6 and chemicalformula 7 after baking is applied on the glass substrate 7 by a spincoating process as the variable wettability layer 2. Thereafter, bakingis conducted at 280°.

[0259] In order to evaluate the characteristics of the variablewettability layer 2, following experiments were conducted separately.

[0260] (1) By using an UV lamp for an optical source, the distancebetween the optical source and the substrate is adjusted such that thereis realized an optical intensity of 5 mW/cm² at the wavelength of 250 nmon the substrate. Next, the radiation doze is changed by changing theduration of irradiation for the wavelength of 250 nm and the change ofcontact angle of the layer 2 to water is observed.

[0261]FIG. 11 shows the relationship between the ultraviolet irradiationdose and the contact angle to water.

[0262] Referring to FIG. 11, it can be seen that the contact angleexceeds 90 degrees in the state where there is no irradiation doze, andthe layer 2 shows hydrophobic (repellent) nature in this state. When theradiation dose is increased to 10 J/cm2 or more, on the other hand, itcan be seen that the contact angle is reduced to about 20 degrees. Inthis state, the layer 2 shows hydrophilic nature.

[0263] Further, it is believed that the foregoing radiation dose can bereduced by appropriately choosing the optical source in correspondenceto the optical wavelength most effective for inducing the foregoingchange of wettability.

[0264] (2) Further, measurement of contact angle has been made forseveral liquids of different surface energy values for the state inwhich the foregoing ultraviolet radiation is applied with the dose of 9J/cm2 and for the state in which no irradiation has been made.

[0265] From FIG. 3, it can be seen that the critical surface tensiontakes the value of about 24 mN/m in the case no irradiation is made andabout 45 mN/m in the case the ultraviolet irradiation is made.

[0266] Next, a mask carrying a pattern with an opening width of 40 μmand the space between the openings of 5 μm is attached to the variablewettability layer 2 and exposure is made by the ultraviolet radiationwith the dose of 9 J/cm².

[0267] Next, by using an ink-jet process, an aqueous solution of PEDOT,a conductive polymer, and PPS is supplied to the variable wettabilitylayer 2. After drying, the source electrode 5 a and the drain electrode5 b are formed.

[0268] Next, a solution in which poly-3-hexylthiophen, a polymersemiconductor, is dissolved into chloroform is applied by a spin coatingprocess, and the semiconductor layer 6 is formed after drying. Further,a solution in which PVP is dissolved in n-butanol is applied by a spincoating process. After drying, the gate insulation film 32 is formed.

[0269] Finally, the gate electrode 33 of PEDOT/PPS is formed by ink-jetprocess.

[0270] The TFT (electron device 31) thus fabricated shows the mobilityof 1.1×10⁻³ cm²/Vs and the On/Off ratio of 120, while these results areby no means inferior to the case of forming the source electrode 5 a andthe drain electrode 5 b by way of lift off process of an Au film formedby evaporation deposition process.

Comparative Example 1

[0271] In Comparative Example 1, the source electrode 5 a and the drainelectrode 5 b are formed by patterning an Au film formed on the glasssubstrate 7 by an evaporation deposition process by conducting a liftoff process, without providing the variable wettability layer 2.

[0272] Next, a solution in which poly-3-hexylthiophen is dissolved inchloroform is applied to the substrate by a spin coating process,followed by a drying process to form the semiconductor layer 6. Further,a solution in which PVP is dissolved into n-butanol is applied thereonby a spin coating process. After drying process, the gate insulationfilm 32 is formed.

[0273] Finally, the gate electrode layer 33 is formed of PEDOT/PPS byusing an ink-jet process.

[0274] The TFT thus fabricated has the mobility of 1.5×10⁻⁴ cm²/Vs andthe On/Off ratio of 80, while these results are inferior to the case ofExample 1 noted above.

[0275] In the case there exists no variable wettability layer 2, thereis imposed no constraint on the orientation of the alkyl chain of thepoly-3-hexylthiophen, and it is believed that the foregoing decrease ofmobility has been caused because of the failure of aligning themolecular axes of the n-conjugate principal chain.

Example 2

[0276] In Example 2, the precursors that form the structures of chemicalformulae 8-11 below after baking are applied on the glass substrateunder the same condition as Example 1 in the form of a solution mixedwith the precursor of the structure represented by chemical formula 7noted before.

[0277] Next, the contact angle is measured for several liquids ofdifferent surface energies before and after irradiation of ultravioletradiation with the dose of 9 J/cm2, and the critical surface tension isobtained similarly to the case of Example 1.

[0278] The results thereof are summarized in Table 2 below. TABLE 2Formula Formula Formula Formula 8 9 10 11 Before UV 18 mN/m 21 mN/m 26mN/m 28 mN/m irradiation After UV 44 mN/m 43 mN/m 41 mN/m 42 mN/mirradiation

[0279] From Table 2, it can be seen that the critical surface tensiontakes the value of 18-28 mN/m in the case no ultraviolet irradiation ismade while the critical surface tension takes the value of 41-44 mN/mafter the ultraviolet irradiation is made. From this, it will beunderstood that any of these materials can also be used for the materialof the variable wettability layer.

Example 3

[0280] In Example 3, the mixed solution used in Example 2 is applied ona glass substrate under the same film forming condition as Example 4.Next, patterning is conducted under the condition similar to that ofExample 4 and the source and drain electrodes are formed by an ink-jetprocess. After this, the semiconductor layer is formed by a spin coatingprocess while using a polymer 1 represented by chemical formula 12 forthe organic semiconductor material.

[0281] Table 3 below shows comparison of the mobility and On/Off ratiofor the TFT thus fabricated to have the structure shown in FIG. 8. TABLE3 Formula Formula Formula Formula 8 9 10 11 Mobility 4 × 10⁻³ 2 × 10⁻³ 6× 10⁻⁴ 4 × 10⁻⁴ (cm²/Vs) On/Off 2820 1260 860 485 ratio

[0282] Thus, a result similar to the case of Example 4 below that usesthe same organic semiconductor is obtained also in the case of using anyof the polyimide materials such as the polyimide represented by thechemical formulae 8 and 9 in which the constituting unit of theprincipal chain is small and the side chain density in the film issimilar, or the polyimide represented by the chemical formula 10 inwhich the constituting unit of the principal chain is larger and theside chain density in the film is smaller than the material of thechemical formula 8 or 9, or the polyimide represented by the chemicalformula 11 having a different side chain length to the material ofchemical formula 10.

Example 4

[0283] In Example 4, an electron device (TFT) having the structuresimilar to the one shown in FIG. 8 is fabricated.

[0284] More specifically, an Al film is formed on the glass substrate 7by evaporation deposition process with the thickness of 60 nm andpatterned by a photolithographic etching process to form the gateelectrode 42 such that the gate electrode 42 has a width of 40 μm.

[0285] Next, the variable wettability layer 2 is formed similarly to theExample 1 as a gate insulation film, and ultraviolet irradiation isconducted with the dose of 9 J/cm² similarly to Example 2 while pressinga mask having a space of 5 μm between mask openings to the variablewettability layer 2.

[0286] Next, an aqueous solution of conductive polymer of PEDOT/PPS issupplied to the variable wettability layer 2 by using ink-jet process.After drying, the electrode layers 5 a and 5 b are formed.

[0287] Finally, a polymer 1 of an organic semiconductor materialsynthesized according to the scheme represented by the chemical formula12 below is applied by a spin coating process in the form of a solutiondissolved in toluene.

[0288] The polymer 1 can be synthesized as follows.

[0289] First, 0.852 g (2.70 mmol) of dialdehyde and 1.525 g (2.70 mmol)of diphosphonate are placed in a four mouth flask of 100 ml capacity.After substituting with nitrogen, 75 nm of tetrahydrofuran is added.Next, 6.75 ml (6.75 mmol) of a 1.0 moldm ³ tetrahydrofuran solution ofpotassium t-butoxide is dripped, and after stirring at room temperaturefor two hours, benzylphosphonate and benzaldehyde are addedsequentially. After stirring for two more hours, the reaction isterminated by adding about 1 ml of acetic acid, and the solution iswashed with water. After removing the solvent under reduced pressure,purification process is conducted by re-precipitation by usingtetrahydrofuran and methanol. With this, 1.07 g of the polymer isobtained. In this case, the yield is 73% (7.93%); N is 2.33% (2.45%).

[0290] The differential scanning thermal analysis showed the glasstransition temperature of 117°. Further, the number average molecularweight equivalent of polystyrene measured by GPC was 8500 and the weightaverage molecular weight was 20000.

[0291] It was shown that the TFT (electron device 41) fabricated in thisway has the mobility of 2.5×10⁻³ cm²/Vs and On/Off ratio of 1350, whilethese results were by no means inferior to the case in which the sourceand drain electrodes 5 a and 5 b are formed by lift off of an Au filmformed by evaporation deposition process.

Comparative Example 2

[0292] In Comparative Example 2, a thermal oxide film is formed on alow-resistance Si substrate as the gate insulation film, and the sourceelectrode layer 5 a and the drain electrode layer 5 b are formed by liftoff patterning of the Au film formed by evaporation deposition process.Otherwise, the device is formed similarly to Example 5.

[0293] The TFT thus formed showed the mobility of 9.8×10⁻⁵ cm²/Vs andthe Of/Off ratio of 1050, while these results are inferior to the caseof Example 4. It is believed that because of the hydrophilic nature ofthe gate insulation film surface, there has occurred increase of surfacestate density as a result of localized polarization, and this increaseof the surface state density has caused the decrease of the carriermobility.

Example 5

[0294] Example 5 relates to manufacturing of the electron device array51 shown in FIG. 9.

[0295] First, the gate electrode 42 and the variable wettability layer 2acting as the gate insulation film are formed similarly to Example 4.Further, the source electrode layer 5 a and the drain electrode layer 5b are formed by using an aqueous solution of PEDOT/PSS, which is aconductive polymer.

[0296] Finally, a solution that dissolves the foregoing polymer 1 intotoluene is used to form the semiconductor layer 6 in the form of islandby using micro contact printing process.

[0297] With the foregoing, a 32×32 two-dimensional array 51 of the TFT(electron device) 41 is formed on the substrate 7. It turned out thatthese TFTs (electron devices) 41 have the average characteristics of1.5×10⁻³ cm²/Vs for the mobility and 970 for the On/Off ratio.

Example 6

[0298] Example 6 related to manufacturing of the display device 61 shownin FIG. 12 that uses the electron device array 51.

[0299] First, microcapsules 67 holding therein titanium oxide particles65 and Isopar 66 (trade name of Exxon) colored with oil blue are mixedin an aqueous solution of PVA as the display element 64, and the aqueoussolution is applied on a polycarbonate substrate 23 carrying thereon thetransparent electrode 62 of ITO. With this, a layer including the microcapsules 67 and the PVA binder 68 is formed. Further, this substrate isbonded together with the substrate 7 carrying thereon the TFT array(electron device array 51) formed according to the process of Example 5.

[0300] Further, a driver IC for the scanning signals is connected to thebus lines each leading to a gate electrode 42 and a driver IC for thedata signals is connected to the bus lines each leading to a sourceelectrode 5 a. With switching of the screen conducted 0.5 seconds each,it was confirmed that good representation of still picture is achieved.

[0301] Further, the present invention is by no means limited to theembodiments described heretofore, but various variations andmodifications may be made without departing from the scope of theinvention.

What is claimed is:
 1. A layered structure comprising: a variablewettability layer including a material that changes a critical surfacetension in response to energy provided thereto, said wettabilitychanging layer comprising at least a high surface energy part of largecritical surface tension and a low surface energy part of low criticalsurface tension; a conductive layer formed on said variable wettabilitylayer at said high surface energy tension part; and a semiconductorlayer formed on said variable wettability layer at said low surfaceenergy part.
 2. The layered structure as claimed in claim 1, whereinthere exists a difference of critical surface tension of 10 mN/m or morein said variable wettability layer between said low surface energy partand said high surface energy part.
 3. The layered structure as claimedin claim 1, wherein said low surface energy part of said variablewettability layer has a critical surface tension of 40 mN/m or less. 4.The layered structure as claimed in claim 1, wherein said variablewettability layer is formed of two or more materials.
 5. The layeredstructure as claimed in claim 1, wherein there is provided adistribution of materials in said variable wettability layer in athickness direction thereof.
 6. The layered structure as claimed inclaim 1, wherein said variable wettability layer comprises at least afirst material having relative excellence in electric insulation and asecond material having relative excellence in the magnitude of change ofthe critical surface tension in response to energy provided thereto. 7.The layered structure as claimed in claim 1, wherein said variablewettability layer comprises a polymer material having a hydrophobicgroup on a side chain.
 8. The layered structure as claimed in claim 7,wherein said polymer material comprises a polymer material includingpolyimide.
 9. The layered structure as claimed in claim 1, wherein saidsemiconductor layer comprises an organic semiconductor.
 10. The layeredstructure as claimed in claim 1, wherein ultraviolet radiation isprovided as said energy that causes a change of the critical surfacetension.
 11. A method of forming a layered structure, comprising thesteps of: forming a variable wettability layer by a material thatchanges a critical surface tension thereof in response to energyprovided thereto; forming a pattern by providing energy to a part ofsaid variable wettability layer such that said variable wettabilitylayer includes a low surface energy part having a low critical surfacetension and a high surface energy part having a high critical surfacetension; forming a conductive layer on said high energy surface part ofsaid variable wettability structure by providing a liquid containing aconductive material to a surface of said variable wettability layerformed with said pattern; and forming a semiconductor layer on said lowenergy surface part of said variable wettability structure.
 12. Themethod as claimed in claim 11, wherein said liquid containing saidconductive material is applied to said surface of said variablewettability layer by an ink-jet process.
 13. The method of as claimed inclaim 11, wherein ultraviolet radiation is used as said energy forcausing change of the critical surface tension.
 14. An electron devicecomprising a layered structure, said layered structure comprising: avariable wettability layer including a material that changes a criticalsurface tension in response to energy provided thereto, said wettabilitychanging layer comprising at least a high surface energy part of largecritical surface tension and a low surface energy part of low criticalsurface tension; a conductive layer formed on said variable wettabilitylayer at said high surface energy tension part; and a semiconductorlayer formed on said variable wettability layer at said low surfaceenergy part.
 15. The electron device as claimed in claim 14, whereinsaid conductive layer forms a pair of electrode layers, said electrondevice further comprising an insulator layer adjacent to thesemiconductor layer and a further electrode layer adjacent to theinsulator layer.
 16. The electron device as claimed in claim 14, whereinthe variable wettability layer is provided on an electrode layer, thesemiconductor layer is provided on the variable wettability layer, andwherein the conductive layer forms a pair of electrodes adjoining thesemiconductor layer.
 17. A method of fabricating an electron device ofthe fifteenth aspect or sixteenth aspect, comprising the steps of:forming a pattern including a lower surface energy part and a highsurface energy part by providing energy to a part of the variablewettability layer; forming a pair of electrode layers on the highsurface energy part by providing a liquid containing a conductivematerial to a surface of the variable wettability layer formed with thepattern; and forming the semiconductor layer on the variable wettabilitylayer.
 18. The method as claimed in claim 17, wherein the liquidcontaining the conductive material is provided to the surface of thevariable wettability layer by an ink-jet process.
 19. The method asclaimed in claim 17, wherein the energy for causing change of thecritical surface tension is provided by way of irradiation ofultraviolet radiation.
 20. An array of electron devices comprising aplurality of electron device, each of said electron devices having alayered structure and comprising: a variable wettability layer includinga material that changes a critical surface tension in response to energyprovided thereto, said wettability changing layer comprising at least ahigh surface energy part of large critical surface tension and a lowsurface energy part of low critical surface tension; a conductive layerformed on said variable wettability layer at said high surface energytension part; and a semiconductor layer formed on said variablewettability layer at said low surface energy part.
 21. A display devicecomprising an electron device array including a plurality of electrondevices, each of said electron devices having a layered structure andcomprising: a variable wettability layer including a material thatchanges a critical surface tension in response to energy providedthereto, said wettability changing layer comprising at least a highsurface energy part of large critical surface tension and a low surfaceenergy part of low critical surface tension; a conductive layer formedon said variable wettability layer at said high surface energy tensionpart; and a semiconductor layer formed on said variable wettabilitylayer at said low surface energy part.